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List of Solar System objects by radius
This is a list of Solar System objects by size, arranged in descending order of mean volumetric radius. The list can also be sorted according to an object's mass and, for the largest objects, volume and surface gravity. This list contains the Sun, the planets, all known dwarf planets and dwarf planet candidates, the largest asteroids (including the largest for the various sub-populations, such as centaurs and Trojans), all named natural satellites, and a number of other objects of historical or scientific interest, such as comets and near-Earth objects. The ordering is different depending on whether one chooses radius or mass, because some objects are denser than others. For instance Uranus is bigger than Neptune but less massive, and although Ganymede and Titan are larger than Mercury, they have less than half its mass. Some objects in the lower tables, despite their small radii, are more massive than objects in the upper tables because they have a higher density. Several new trans-Neptunian objects (TNOs) have been discovered of significant size. While their radius remains provisional due to the recency of discovery, and is often expressed as a range, the approximate locations in this list are shown. All Solar System objects more massive than 1021 kilograms (one yottagram [Yg]) are known or expected to be approximately spherical. Astronomical bodies relax into rounded shapes (ellipsoids), achieving hydrostatic equilibrium, when the gravity of their mass is sufficient to overcome the structural strength of their material. However, objects made of ice become regular more easily than those made of rock, and many icy objects are spheroidal at far lower masses. The cutoff boundary for regularity appears to roughly coincide with the 200 km radius. The larger objects in the mass range between 1018 kg to 1021 kg (1 to 1000 Zettagrams (Zg)) such as Tethys, Ceres, and Mimas, have relaxed to an equilibrium oblate spheroid due to their gravity, while the less massive rubble piles (e. g. Amalthea and Janus) are roughly rounded, but not spherical, dubbed "irregular". Spheroidal bodies typically have some polar flattening due to the centrifugal force from their rotation, but a characteristic feature of the "irregular"-shaped bodies is that there is a significant difference in the length of their two equatorial diameters. There appears to be difficulty in figuring out the diameter (within a factor of about 2) for typical objects beyond Saturn. (See 2060 Chiron as an example.) For TNOs there is some confidence in the diameters, but for non-binary TNOs there is no real confidence in the "unreferenced wiki-assumed" masses/densities. Many TNOs are just assumed to have a density of 2.0 g/cm³, though it is just as likely that they have a comet like density of only 0.5 g/cm³. Thus most provisional TNOs are not given a MEarth value to prevent from cluttering the list with too many assumptions that could be off by an order of magnitude. For example if a TNO is poorly assumed to have a mass of 3.59 kg based on a radius of 350 km with a density of 2 g/cm³ and is later discovered to only have a radius of 175 km with a density of 1 g/cm³, the mass estimate would be only 2.24 kg. The sizes and masses of many of the moons of Jupiter and Saturn are fairly well known due to numerous observations and interactions of the Galileo and Cassini orbiters. But many of the moons with a radius less than ~100 km, such as Jupiter's Himalia, still have unknown masses with assumed densities. Again, as we get further from the Sun than Saturn, things get less clear. There has not yet been an orbiter around Uranus or Neptune for long-term study of the moons. For the small outer irregular moons of Uranus, such as Sycorax, which were not discovered by the Voyager 2 flyby, even different NASA web pages, such as the National Space Science Data Center and JPL Solar System Dynamics, have somewhat contradictory size and albedo estimates depending on which research paper is being cited. Data for those objects smaller than Miranda are less reliable due to uncertainties in the figures for mass and radius, and irregularities in the shape and density of the objects listed. File:Sun vs planets.png|The relative masses of the bodies of the Solar System. Objects smaller than Saturn are not visible at this scale. File:Masses of the planets.png|The relative masses of the Solar planets. Jupiter at 71% of the total and Saturn at 21% dominate the system. Mercury and Mars, which together are less than 0.1%, are not visible at this scale. File:Masses of Solid Solar System bodies.png|The relative masses of the solid bodies of the Solar System. Earth at 48% and Venus at 39% dominate. Bodies less massive than Pluto are not visible at this scale. List Objects above ~200 km in radius These objects hypothetically lie above the boundary for hydrostatic equilibrium. As such, all manually calculated values assume sphericity. Objects between 200 and 100 km in radius The largest of these objects just might lie above the boundary for hydrostatic equilibrium, but most are irregular. Most of the Trans-Neptunian objects listed with a radius smaller than 200 km have "assumed sizes based on a generic albedo of 0.09" since they are too far away to directly measure their sizes. Volume and surface gravity are difficult to calculate for irregular objects. Values relative to Earth are too inexact to be useful beyond this point. Mass switches from 1021 kg to 1018 kg (Zg), with Mimas double listed as example of unit shift. Main belt asteroids have orbital elements constrained by (2.0 AU < a < 3.2 AU; q > 1.666 AU) according to JPL Solar System Dynamics (JPLSSD). Objects between 100 and 50 km in radius Objects 200 km to 100 km in average diameter. Objects below this point are not massive enough to be rounded by their own gravity. Examples of objects between 50 km and 20 km in radius There are easily tens of thousands of objects 50 km in radius or smaller , but only a fraction have been explored. The number of digits is not an endorsement of significant figures. The table switches from kg to kg (Eg), and many of these mass values are assumed. (see also List of minor planets) Examples of objects between 20 km and 1 km in radius Examples of objects below 1 km (1000 m) In the main asteriod belt alone there is estimated to be between 1.1 and 1.9 million objects with a radius above 0.5 km, many of which are in the range 0.5-1.0 km. Countless more have a radius below 0.5 km. Very few objects in this size range have been explored or even imaged. The exceptions are objects that have been visited by a probe, or have passed close enough to Earth to be viewed by large telescopes. Radius is by mean geometric radius. Number of digits not an endorsement of significant figures. Mass shifts from 1015 to 1012 kg (Pg). Currently all the objects of mass between 109 kg to 1012 kg (less than 1000 Teragrams (Tg)) listed here are Near-Earth asteroids (See also: list of NEAs by distance from Sun.) Note that possesses less mass than the Great Pyramid of Giza, 5.9 × 109 kg Notes :† Using equatorial radius and assuming body is spherical :‡ Using three radii and assuming body is spheroid : * Radius is known only very approximately :R Radius has been determined by various methods, such as optical (Hubble), thermal (Spitzer), or direct imaging via spacecraft :9 Unknown radius, generic assumed albedo of 0.09 :$ Well studied asteroid or moon where the dimensions and mass are very well known. Asteroid sizes and masses taken from James Baer's (Bio) personal website. :M Mass has been determined by perturbation. For asteroids, see James Baer's personal website. :A Assumed mass :P Mass calculated assuming Pluto's density of 2.0 g/cm3 :Note: For many of the well-determined moons, radii were taken from the JPL Solar System Dynamics page. :O Radius has been determined with Asteroid occultation Surface gravity The surface gravity at the equator of a body can in most cases be accurately calculated using Newton's law of universal gravitation and centrifugal force. The gravitational acceleration at the equator is given by Newton's law of universal gravitation. The formula that follows from this law is: : a_g = G \frac{m}{r^2} where :ag is the magnitude of the gravitational acceleration :G'' is the gravitational constant :''m is the mass of the celestial body :r'' is the equatorial radius of the celestial body (if this varies significantly, the mean equatorial radius is used) The magnitude of the outward acceleration due to ''centrifugal force is given by : a_c = 4\pi^2\frac{r}{T^2} where :T'' is the rotation period of the celestial body The surface gravity at the equator is then given by : g = a_g - a_c = \frac{G m}{r^2} - \frac{4\pi^2r}{T^2} References }} Further reading * NASA Planetary Data System (PDS) * Asteroids with Satellites * Minor Planet discovery circumstances * Supplemental IRAS Minor Planet Survey (SIMPS) and IRAS Minor Planet Survey (IMPS) ** SIMPS & IMPS (V6, additional, from here ** Asteroid Data Archive (dead link) Archive ''Planetary Science Institute External links * Planetary fact sheets * Asteroid fact sheet * All (known) Bodies in the Solar System Larger than 200 Miles in Diameter - in an image, put side-by-side. Category:Lists of Solar System objects bg:Списък на обектите в Слънчевата система по радиус fr:Liste des objets du système solaire classés par taille ko:반지름순 태양계 천체 목록 hr:Popis tijela Sunčeva sustava prema promjeru la:Index corporum systematis solaris secundum radium pl:Lista obiektów w Układzie Słonecznym ze względu na promień sl:Seznam teles v Osončju po polmeru zh:太阳系天体半径列表